Two concurrent executing transactions š¯‘‡1 and š¯‘‡2 are allowed to update sameā€¦
2019
Two concurrent executing transactionsĀ š¯‘‡1Ā andĀ š¯‘‡2Ā are allowed to update same stock item sayĀ ā€²Aā€²Ā in an uncontrolled manner. In such scenario, following problems may occur:
(a) Dirty read problem
(b) Lost update problem
(c) Transaction failure
(d) Inconsistent database state
Which of the following option is correct if database system has no concurrency module and allows concurrent execution of above two transactions?
- A.
(a), (b) and (c) only
- B.
(c) and (d) only
- C.
(a) and (b) only
- D.
(a), (b) and (d) only
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Correct answer: D
Answer: Dirty read, Lost update, and Inconsistent database state.
Dirty read: occurs when a transaction reads changes made by another transaction that have not yet been committed, so those reads might later be invalid if the other transaction rolls back.
Lost update: happens when two transactions read the same item and both write updates based on the old value; the later write can overwrite the earlier one, causing one update to be lost.
Inconsistent database state: arises when concurrent uncontrolled updates leave related data or aggregates out of sync (for example, item counts or totals not matching individual item changes).
Why transaction failure is not included:
Transaction failure can occur for many reasons (such as constraint violations or system errors), but uncontrolled concurrency by itself typically produces the data anomalies listed above rather than guaranteeing that a transaction will fail. Therefore, the correct set of problems that are expected when there is no concurrency control are dirty reads, lost updates, and inconsistent database state.
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